reproduces these signals on the chart, resulting in a high contrast re- 

 cording of the bottom profile. This is accomplished by variable ampli- 

 fication with the gain control, threshold to eliminate background noise, 

 and contrast, which allows the amplifier dynamic range to be changed to 

 suit variations in input signal-to-noise ratio. 



The threshold circuit allows the setting of the minimum signal that 

 the recorder will print. If the input is below a predetermined signal 

 level, there will be no output from the print amplifier. If the input 

 goes above this level, the recorder will print a shade determined" by the 

 setting of the gain control. It may be noted that the gain control 

 follows the threshold voltage pick-off point, allowing threshold to be 

 set independently of gain. Full limiting is included to eliminate the 

 possibility of allowing too much energy to reach the stylus, which would 

 result in excessive black printing during the outgoing pulse. 



The contrast control allows the dynamic range of the recording to be 

 varied. This differs from the gain control in that the latter simply 

 varies the absolute input range that will cause the recording to go from 

 white to black. (See Fig 1^ and Fig l6 for sample recordings.) 



The operation of the three controls, in a typical condition (Fig 5), 

 would be as follows: If the input echo, which is usually the main 

 signal of interest, has a dynamic range of lit db, the gain control would 

 normally be set so that the echo: signal peak would print black. Any 

 input signal above this level will not print heavier due to the limiting 

 feature. The threshold control would be set at a point approximately 

 -13 db from the peak input echo; the signal to the power amplifier would 

 then consist of a 13 db input signal variation. The contrast control 

 is next set to give the best quality record which, in this case, would 

 probably be such that the dynamic range of the print amplifier would 

 cause a recording to go from white to black in a range of 13 db. If 

 additional detail of the lower amplitude second echoes is desired, the 

 contrast range would be greater, e.g., 2^ db. AGC has not been included 

 in the present design until adequate sea tests can be completed to in- 

 sure that this function is merited in this application. 



The print amplifier also prints grid marks on the chart, which are 

 generated by the grid marking generator. Interruption of printing for 

 various functions is achieved through the print control lead, which acts 

 as an on-off switch. 



The input impedance of the PFR-193 print amplifier is 5000 ohms, with 

 a constant frequency response from 1 to 20 kc of the processed input. She 

 auxiliary input will accept signals from 10 cps to 100 kc ;to permit print- 

 ing of auxiliary inputs enabling the recorder to check external functions. 

 A typical application might be to record the ticks of a watch, checking 

 its accuracy. Available as an option is a facsimile converter which 

 converts the PFR-193 to standard 120-rpm facsimile recorder, when used 

 in a standard facsimile communication network. 



188 



